Backup Commands: Before you take the backup, ensure the Site has 'none' lock. However, when you are ready to run the backup... make sure you make the site lock to 'readonly' so that no further changes can occur.

Output: In case the target site does not exist Restore commands would create a new site collection (if it were a different server). If restoring on the same server, you have to use '-override' parameter or have to create a new content database for that Site Collection and then restore.